The present invention relates in general to the semiconductor processing field and, in particular, to a low voltage fuse element and method of fabrication.
Certain semiconductor devices, such as dynamic random access memories (DRAMs) and static RAMs (SRAMs), are designed with redundant rows and/or columns of memory bits. The redundant rows and columns can be connected into a memory array to substitute for memory cells found defective during the testing and inspection process. This connection can be made by blowing selected fuses that are strategically located in the memory array and the redundant rows and columns. Typically, these fuses are made of polysilicon formed on a field oxide layer simultaneously with a gate electrode. Alternatively, these fuses can be made of a metal material.
A significant problem experienced with conventional polysilicon fuses is that they have relatively high inherent and parasitic resistances. On the other hand, the current required to blow such a polysilicon fuse is relatively low. A significant problem experienced with conventional metal fuses is that they require exceedingly high currents to make them blow. However, the inherent resistance of such metal fuses is relatively low.
Accordingly, there is a need for a fuse element with low inherent resistance, which also requires a low amount of current to melt the fuse element and make it blow.
In accordance with the present invention, a fuse element and method of construction are provided that eliminate or substantially reduce the disadvantages and problems associated with prior fuse elements.
In one embodiment of the present invention, a fuse element is constructed with a rectangular-shaped contact. The contact is made long enough so that it makes contact at each end with a metal layer, but design rule spacing is still maintained between the connections with the metal layer. In this embodiment, a polysilicon plate under the fuse element is primarily to land the contacts and does not carry any of the fusing current. In one aspect, the overlapping areas between the rectangular contact and the metal layers are selected to be asymmetrical. Alternatively, in another aspect, one or more of these overlapping areas is selected to be smaller than the design rule overlap requirements.
In a second embodiment of the present invention, a fuse element is constructed with a plurality of rectangular-shaped contacts. In this case, the overlapping areas of the metal layer and contacts are selected to be asymmetrical. In this embodiment, the polysilicon supports the fusing element, but is not the fusing element.
An important technical advantage of the present invention is that a fuse element is provided which has significantly lower inherent resistance and parasitic resistance than prior polysilicon fuses.
Another important technical advantage of the present invention is that a fuse element is provided which requires a significantly lower amount of current to blow than prior metal fuses.
Still another important technical advantage of the present invention is that a fuse element is provided which requires a significantly lower blow voltage than that used for prior fuses.
Yet another important technical advantage of the present invention is that a fuse element is provided with a small overlap area between a contact and a metal layer, which can generate very high interfacial current densities in a relatively compact layout.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description and claims.